Sodium bicarbonate is an important industrial chemical useful in water and air pollution control, various industrial processes, and in higher grades as an agricultural feed additive and component of foods.
There are three basic processes for production or recovery of bicarbonate: (1) The carbonation of naturally or synthetically-produced sodium carbonate solutions; (2) crystallization of a naturally occurring or by-product sodium bicarbonate solution; and (3) carbonation of ammonium carbonate and reacting with sodium chloride. A natural sodium carbonate is carbonated to produce sodium bicarbonate by Kerr-McGee at Searles Lake, Calif., ICI in Africa and a Mexican plant near Mexico City. Synthetic or naturally produced sodium carbonate is carbonated to produce sodium bicarbonate by Church and Dwight Company in New York, Ohio and Wyoming, by Stauffer Chemicals Company in Illinois and by Riverside Products Company in Georgia. ICI in England, Allied Chemical in Canada and Solvay in Western Europe employ the ammonium bicarbonate/sodium chloride process to produce synthetic sodium bicarbonate.
Natural sodium bicarbonate has been crystallized by Dennison Resources in Australia. The process, involving carbonation of natural sodium carbonate solutions, is practical because the sodium carbonate solution is usually a saturated brine solution containing a variety of sodium salts. The solubility of sodium bicarbonate is greatly depressed by the presence of sodium chloride, sodium sulfate or other salts. In such brines, the sodium carbonate concentration is typically 3-7% by weight. The resulting sodium bicarbonate solubility is typically only 1-2% by Thus a 5% sodium carbonate solution may be carbonated to a 0.5% sodium carbonate/7.15% sodium bicarbonate solution; 85% of the bicarb precipitates, and 82% sodium carbonate recovery is realized.
There are vast quantities of Nahcolite deposits in the Piceance Creek Basin in Northwestern Colorado, which deposits are in the form of beds and disseminated crystals in the Saline Zone of the Green River formation. This zone is more well known for the presence of large quantities of oil shale. The entire zone ranges on the order of 1,000 feet thick with relatively high concentrations of kerogen capable of producing from 12 to 30 gallons of oil per ton. Interbedded in the formation are beds and zones of disseminated crystals of various sodium minerals, including Halite (NaCl), Nahcolite, Dawsonite, and Wegeschiderite.
U.S. Pat. No. 3,779,602 of Beard et al. (Shell Oil Co.) proposes to solution mine sodium bicarbonate minerals from an oil shale formation by injecting steam at the top of a predominantly steam-filled cavity at a temperature greater than 250.degree. F., and maintaining the cavity temperature greater than 250.degree. F., preferably greater than 300.degree. F. to maximize cavity growth rate. Condensation of steam to a liquid form is said to occur on contact with the formation resulting in collection of superheated water in the lower portion of the cavity. The pressure is adjusted and maintained to an optimum pressure at which the sodium-carrying capacity of the superheated water at the selected high temperature is a maximum. Below this pressure there will be excess thermal decomposition of bicarbonate to carbonate and precipitation of carbonate. Above this pressure conversion of bicarbonate to carbonate is inhibited and the mineral-carrying capacity of the leaching fluid is reduced. The aim is to remove the most sodium mineral per gallon, and this perforce is a mixture of sodium bicarbonate and carbonate. At 400.degree. F. the patent calls for a cavity pressure of 1000 psi. The cavity growth is predominantly temperature dependant, the patent in Col. 21 66-67 stating "cavity growth rate is only slightly dependant on rate of fluid injection", due to thermal fracturing of the oil shale surrounding the Nahcolite nodules. Beard has stated publicly that Shell Oil disposed without any processing by down well injection of all sodium solutions produced in the Shell experiments. This Shell patent is directed to a quite different process in a different formation, using pressurized steam in a Nahcolitic oil shale zone containing 20-40% of disseminated nodular Nahcolite crystals, and also containing a few stringers of substantially pure Nahcolite.
Towell et al., of Shell Oil in U.S. Pat. No. 3,792,902 injects hot water of low alkalinity into the base of the production tubing string or adjacent the intake to prevent mineral precipitation and plugging of the production well by dilution. The patent is directed to recovery by solution mining of trona or Nahcolite by use of hot water or steam (for example, at a temperature of 325.degree. F. and pressure of 1500 psi) to produce a mixed Na.sub.2 CO.sub.3 /NaHCO.sub.3 -rich production solution. As in Beard 3,779,602 there is a pressure/temperature dependency relationship which in this patent is related to dilution ratio to prevent precipitation in the production tubing. For example, for a 2:1 dilution ratio the dilution fluid is 220.degree. F. to 530.degree. F. while the production fluid is in the range of 300.degree. F.-480.degree. F. Pressures of 500-800 psi are disclosed as the operating range.
Beard of Shell Oil in U.S. Pat. No. 3,759,574 teaches a method producing shale oil from trona and/or Nahcolite mineral bearing oil shale formations which process includes an initial step of permeabilization of the formation by dissolution of the sodium minerals with a hot aqueous solution. Similarly, Kelmar in U.S. Pat. No. 4,375,302, as part of multi-mineral recovery from oil shale, proposes to inject an NaOH solution into oil shale to dissolve NaHCO.sub.3 and convert it to an Na.sub.2 CO.sub.3 solution. This is to develop porosity in the oil shale as a step in preparation for recovery of shale oil via in-situ retorting of rubbed oil shale.
Uber et al. of Shell Oil in U.S. Pat. No. 3,759,328 expands a cavern (e.g. a bore hole) in an oil shale formation by use of steam, hot water or a mixture thereof, to permeabilize and rubble the oil shale rock for subsequent recovery of shale oil through pyrolysis of the kerogen contained in the oil shale. The steam is introduced at the top of the cavern, and the pressure is maintained above the decomposition pressure of the carbonate minerals (trona or Nahcolite). The temperature ranges from above about 250.degree. F. up to 600.degree.-1000.degree. F., i.e. enough to cause a relatively rapid oil shale pyrolysis. Decomposition of the minerals is taught, and shale oil is extracted along with the outflowing fluid from the production pipe. This patent is after the oil, not the sodium minerals.
Papadopoulos et al. of Shell Oil in U.S. Pat. No. 3,700,280 enlarges bore hole "cavern" in oil shale containing low grade Nahcolite (5-40%) and Dawsonite (10-12%) by injecting a hot fluid (steam or hot water) in the upper region of the "cavern" at a temperature hot enough to cause decomposition of the Nahcolite and Dawsonite to form CO.sub.2 and water, thereby building up enough pressure to cause fracturing and rubbling of the cavern roof. This is a process of in situ gas fracing by decomposition Nahcolite and Dawsonite. Recovery of NaHCO.sub.3 is not taught. This patent, states in passing (column 4, lines 41-44): "Into an oil shale formation rich in Nahcolite and Dawsonite a well was completed at below about 2000 feet and a portion of the Nahcolite bed was water leached to form a cavern. Steam was injected along the cavern roof to decomposition [sic]the Nahcolite and Dawsonite to form carbon dioxide thereby building up pressure and cause upward migration of the cavern roof and oil shale rubbling."
It is known that powdered sodium bicarbonate injected in the flue gas of a power as industrial plant serves as an excellent sorbent for removal of SO.sub.x and NO.sub.x therefrom. The dry powdered sodium bicarbonate is effective in removing SO.sub.x and NO.sub.x, while Trona (or sodium sesquicarbonate) is less effective, and sodium carbonate is, practically speaking, ineffective. However, the cost of commercially available sodium bicarbonate is prohibitive.
Thus, there is a great need in the art to provide a low cost source of powdered crystalline sodium bicarbonate for use as an air pollution control sorbent. Only through a development of a process and apparatus for recovery of dissolved sodium bicarbonate from solution-mined Nahcolite deposits can there be made available low cost powdered crystalline sodium bicarbonate for air pollution control sorbents and other conventional sodium bicarbonate uses.